The invention relates to a piston usable to actuate transmission bands, and particularly to a piston of a pressure-responsive actuator having a piston rod of adjustable effective length.
In a known piston of this type (U.S. Pat. No. 3,554,057), the receiving bore per se is open at both ends, and a threaded bolt is screwed into the receiving bore, as a stop for the piston rod, from the mouth located opposite the piston-rod end designed as a thrust piece, and is secured by means of a lock nut. So that aluminum can be used as the material for the piston, the guide having the threaded portion for the stop and the actual piston body have to be made in two parts, and at least an additional retaining ring is necessary for fixing the guide and piston body relative to one another.
In known pistons of a different type, in which either no guide or a guide integral with the housing is used and the piston rod is not adjustable in terms of its effective length, the piston and piston rod are either screwed (U.S. Pat. No. 3,327,554) or riveted (special issue of ATZ Automobiltechnische Zeitschrift, 72nd year, numbers 7 and 9, 1970 Franckh's sche Verlagshandlung Stuttgart, page 12, FIG. 26). The stock-keeping of these known pistons involves a high outlay, because a large number of piston rods of different lengths have to be kept in stock.
The disadvantage of expensive stock-keeping is also a characteristic feature of a known brake-band actuation system of a different type (German Unexamined Published Patent Application 3,012,611), in which tolerances are compensated by the selection of a reaction thrust piece of suitable effective length from a plurality of reaction thrust pieces of different lengths. In this case, the reaction thrust piece is inserted operatively between the gear box housing and one brake-band end, while a piston acts in turn on the other brake-band end by means of a nonadjustable piston rod which slides in guide integral with the housing and which is fixed to the piston in one axial direction by means of a retaining ring. There also operates in the cylinder housing of the piston a spring-loaded release piston, through which the piston rod passes displaceably and which needs to be sealed off in a pressure-tight manner from both the inner wall of the cylinder housing and the piston rod.
The object on which the invention is based is essentially to provide a piston which has a piston rod of adjustable effective length and which is distinguished by a low outlay in terms of construction. An important advantage of the piston according to the present invention is that the effective length is fixed by means of the compensating washer or compensating washers, in such a way that it is not possible to vary it by breaking the connection between the piston and the piston rod, as is the case in the known piston with a threaded bolt as a stop for the piston rod, when the threaded bolt is rotated after the lock nut has been released. A new measuring and adjusting operation is then necessary on the known piston. A further advantage is simply handling when play is compensated in production.
According to preferred embodiments of the present invention, a piston for actuating a brake-band end of a transmission band system includes a piston for actuating a band in a transmission. The piston includes a piston body, and an elongated guide shaft having a proximal end fixed to one side of the piston body and a distal end defining a first annular support surface. The guide shaft is formed to include an axial bore having an opening in the first annular support surface. The piston further includes a piston rod having an outer end for engaging the transmission band, an inner end for reception in the axial bore, and a second annular support surface situated to confront the first annular support surface when the inner end of the piston rod is received in the axial bore of the elongated guide shaft. An O-ring is positioned along the inner end of the piston rod, to retain said inner end within the axial bore of the elongated shaft. At least one spacer mean is situated intermediate the first and second annular support surfaces to separate said annular support surfaces to vary the effective length of the piston rod.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purpose of illustration only, an embodiment in accordance with the present invention.